Friction stir welding method and group of shape members for friction stir welding

ABSTRACT

The purpose of the present invention is to provide a method that can be easily applied to friction stir welding where the thickness of face plates at one welding portion is different from the thickness of face plates at another welding portion. Three shape members  10, 11, 12  having two butt joint portions are mounted on a jig  15 . The face plate  14  of shape member  10  is thick and the face plate  14  of shape member  12  is thin. The protruded height of projection  18  is greater at portion B where surface plates  14  being welded are thin than the protruded height of projection A where surface plates  14  are thick. The depths for inserting rotary tools to shape members  10, 11, 12  for friction stir welding are the same. Friction stir welding is facilitated since the size and insertion depth of all the rotary tools being applied can be the same.

The present application claims priority from Japanese patent applicationJP2003-312669 filed on Sep. 4, 2003, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to a friction stir welding method, and toa group of shape members for friction stir welding.

DESCRIPTION OF THE RELATED ART

Friction stir welding is a method for inserting a rotary tool having asmall diameter portion and a large diameter portion to a butted jointportion of aluminum shape members, and stirring, softening andplasticizing the same to carry out solid-phase welding thereof, asdisclosed in patent document 1.

In the above disclosure, projections that protrude toward the thicknessdirection of a plate-shaped member are formed to the ends of themembers, and the rotary tool is inserted from the side having theprojections so that when a gap exists in the butted portion, the gap canbe filled with the metal material constituting the projections. Someportions of the projections remain on the joint portion, so aftercompleting the friction stir welding, the remaining projections areremoved by a grinder.

The width of each shape member is approximately 30 cm to 40 cm, so inorder to form a member having a larger width, plural shape members arewelded together. The heights of the projections on the shape members arethe same.

Patent Document 1: Japanese Patent No. 3014654

However, when considering the actual application of the friction stirwelding method to a structure of a railway car, the thickness of theplate members constituting the railway car varies in different areas,and the height of the small diameter portion of the rotary tool must besubstantially equal to the thickness of the plate member being welded.Therefore, rotary tools having different sizes must be usedappropriately to correspond to various welding areas, which make thehandling and management of the rotary tools troublesome.

The prior art method will be described in detail with reference to FIGS.7 through 9. A side framing of a railway car is shown, and in thedrawing, three shape members (hollow shape members) 10, 11 and 12 arebutted against one another and mounted on a jig 15. Though the number ofshape members used for building the actual railway car structure is muchgreater, the present example describes three members. There are twowelding portions, A and B. Each shape member 10, 11, 12 has a rib 17disposed on the upper surface of a face plate 14 for reinforcement, butin the drawing, only the rib 17 on the shape member 11 is illustrated,and the ribs on the other members 10 and 12 are not shown. Areinforcement member (not shown) is welded onto the rib. A projection 18that protrudes toward the outer direction of thickness (upper directionin FIG. 7) of the face plate 14 is formed at each of the buttingportions on the width-direction ends of the shape members 10, 11, 12.

The thickness of the face plate 14 of the shape member 10 is thickerthan the thickness of the face plate 14 of other shape members 11 and12. This is because the shape member 10 has a window (not shown) but theother shape members 11 and 12 do not. Therefore, the face plate 14 ofthe center shape member 11 is designed so that the side attached to theshape member 10 has a thickness corresponding to the face plate 14 ofshape member 10, and the side attached to the shape member 12 has athickness corresponding to the face plate 14 of shape member 12.

The protruded heights of the projections 18, 18 at a butt joint portionA between the shape members 10 and 11 are the same. The widths of theprojections 18, 18 are also the same. The protruded heights of theprojections 18 are determined so that during friction stir welding, theboundary 33 between the large diameter portion 31 and the small diameterportion 32 of the rotary tool 30 is positioned within the projections18. If the overlap margin of the small diameter portion 32 and theprojections 18 is zero (that is, if the boundary 33 is located along theextension of the outer surface of face plate 14), the outer surface ofthe face plate 14 will be dented, so in order to overcome this problem,the boundary 33 is located inside the projections 18. The length of thesmall diameter portion 32 is determined so that the head portion of thesmall diameter portion 32 is located near the back surface of the faceplate 14 (or the jig 15) during friction stir welding.

The heights and widths of projections 18, 18 at a butt joint portion Bbetween the shape members 11 and 12 are the same, which are also equalto the size of the projections on shape members 10 and 11. Friction stirwelding is performed so that the boundary 33 between the large diameterportion 31 and the small diameter portion 32 of the rotary tool 30 ispositioned within the projections 18. The length of the small diameterportion 32 is determined so that the head portion of the small diameterportion 32 is located near the back surface of the face plate 14 (or thejig 15) during welding.

One example of the plate thickness of the face plate 14 will bedescribed, wherein the thickness of the face plate 14 of the shapemember 10 is 4 mm, the thickness of the face plate 13 of the shapemember 12 is 3 mm, and the thickness of the face plate 14 of the shapemember 11 at the end adjacent to the shape member 10 is 4 mm and the endadjacent to the shape member 12 is 3 mm. The protruded height of theprojections 18 at butt joint portion A is 2 mm, and the protruded heightof the projections 18 at butt joint portion B is 2 mm. The width of theprojections 18 is 6.5 mm.

According to such example, the rotary tool 30 for welding the butt jointportion A must have a small diameter portion 32 with a length of 5 mm,and the rotary tool 30 for welding the butt joint portion B must have asmall diameter portion 32 with a length of 3 mm, so it is necessary toprepare rotary tools 30 having small diameter portions 32 with differentlengths to correspond to the butt joint portions A and B.

As explained, if there are plural areas to be subjected to friction stirwelding, a variety of rotary tools must be prepared to correspond to theareas to be welded.

Therefore, the object of the present invention is to enable a rotarytool 30 of a single size to correspond to all the areas to be welded.

SUMMARY OF THE INVENTION

The object of the present invention is achieved by a friction stirwelding method comprising preparing plural members, each havingprojections at end portions of a plate that protrude toward a directionof thickness of the plate; butting an end portion of the plate againstan end portion of an adjacent plate, wherein the thickness of the plateof at least one member is different from the thickness of the plate ofanother member, and the protruded height of the projections on theplates at a butt joint portion where the plate thickness is large issmaller than the protruded height of the projections on the plates wherethe plate thickness is small, and the protruded height of theprojections on the plates at a butt joint portion where the platethickness is small is larger than the protruded height of theprojections on the plates where the plate thickness is large; andinserting rotary tools of the same size with the same insertion depth tothe plates from the side having the projections, and performing frictionstir welding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view showing a side framingsubjected to friction stir welding according to one embodiment of thepresent invention;

FIG. 2 is a vertical cross-sectional view of portion A of FIG. 1;

FIG. 3 is a vertical cross-sectional view of portion B of FIG. 1;

FIG. 4 is a front view of a side framing subjected to friction stirwelding according to another embodiment of the present invention;

FIG. 5 is a vertical cross-sectional view of portion A of FIG. 4;

FIG. 6 is a vertical cross-sectional view of portion B of FIG. 4;

FIG. 7 is a front view of a side framing subjected to friction stirwelding according to the prior art;

FIG. 8 is a vertical cross-sectional view of portion A of FIG. 7; and

FIG. 9 is a vertical cross-sectional view of portion B of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention will now bedescribed.

Embodiment 1

A first embodiment of the present invention will be described withreference to FIGS. 1 through 3. In FIG. 1, the thicknesses of the faceplates 14 of shape members 10, 11 and 12 are the same as the exampleillustrated in FIG. 7. The thickness of the face plate 14 of shapemember 10 is 4 mm, the thickness of the face plate 14 of shape member 12is 3 mm, and the thickness of the face plate 14 of shape member 11 is 4mm at the side adjacent to the shape member 10 and 3 mm at the sideadjacent to the shape member 12.

The protruded height of projections 18, 18 at butt joint portion Abetween the shape member 10 and the shape member 11 is 2 mm, and theprotruded height of projections 18, 18 at butt joint portion B betweenthe shape member 12 and the shape member 11 is 3 mm, according to whichthe protruded height of the projections 18 at joint portion B is greaterthan the protruded height of the projections 18 at joint portion A.Thus, the thicknesses including the projections 18 and the face plate 14of the plural shape members 10, 11 and 12 are all the same.

The lengths of the small diameter portions 32 of the rotary tools 30 forwelding all the joint portions A, B are the same. That is, the length ofthe small diameter portion 32 of the rotary tool 30 for welding jointportion B is the same as that of the rotary tool 30 for welding jointportion A. The length of the small diameter portion 32 is greater thanthe thickness of the face plate 14 where the plate thickness isgreatest. Actually, if the plate thickness 14 at portion A where theface plate thickness is greatest is 4 mm, the length of the smalldiameter portion 32 of the rotary tool is 5 mm, and the overlap marginof the projection 18 and small diameter portion 32 is 1 mm. If the platethickness where the thickness is smallest is 3 mm, the overlap margin ofthe projection 18 and small diameter portion 32 is 1 mm. The externalshape of the large diameter portions 31 of the rotary tools 30 forwelding joint portions A and B are the same. The external shape of thesmall diameter portions 32 thereof are also the same.

According to such arrangement, rotary tools 30 having theabove-mentioned size are disposed at joint portions A and B, andfriction stir welding is performed. Even at joint portion A where theplate thickness is greatest, the insertion depth of the small diameterportion 32 of the rotary tool is the same as that of the prior artexample, so friction stir welding can be performed in a similar manneras according to the prior art.

At joint portion B where the plate thickness is smallest, the boundarybetween the small diameter portion 32 and the large diameter portion 31is placed 1 mm below the upper surface of the projection 18 whileperforming friction stir welding. The insertion depth of the smalldiameter portion 32 of the rotary tool 30 is controlled to be the sameat all times. The boundary is placed 1 mm below the upper surface atboth joint portions A and B.

Thus, there is no need to change the size of the rotary tool 30 forwelding joint portions A and B, and the insertion depth of the rotarytool 30 can be the same.

Therefore, the welding operations can be facilitated.

If the side provided with the projections 18 constitutes the outer sideof the car body, the projections 18 are cut and removed after completingfriction stir welding, so that the joint portion constitutes a flatsurface with the outer surface of the plate 13.

According to the above-mentioned embodiment, rotary tools are disposedat all the joint portions, and friction stir welding operations areperformed simultaneously at all the joint portions, but it is alsopossible to perform friction stir welding of one joint portion A, andthen thereafter, perform friction stir welding of the other jointportion B using the same rotary tool 30 used to weld joint portion A.

The present invention is applicable not only to extruded members made ofaluminum but also to other members.

Embodiment 2

The first embodiment utilized a single-skin shape member, but thepresent invention can be applied to a double-skin shape member (hollowshape member). The welding depth of a rotary tool 30 cannot be definedclearly since the back surface of the joint portion of hollow shapemembers is not in contact with a jig 15, but basically, the depth issubstantially equal to the plate thickness.

In FIG. 4, each of the hollow shape members 100, 110 and 120 is composedof two substantially parallel face plates 13 and 14, connecting plates16 and 17 that connect the face plates 13 and 14, and projections 18formed at width-direction ends of the shape member. The thicknesses ofthe face plates 13 and 14 of shape members 100, 110 and 120 are the sameas the thicknesses of the face plates 14 illustrated in FIG. 1. Thethickness of the face plates 13 and 14 of the shape members 100 isgreater than the thickness of the face plates 13 and 14 of the shapemember 120 (in other words, the thickness of the face plates 13, 14 ofshape member 120 is small). The thickness of face plates 13 and 14 ofthe shape member 110 near a joint portion B with the shape member 120 issmall, whereas the thickness of face plates 13 and 14 of the shapemember 110 near a joint portion A with the shape member 100 is large.

The projections 18 of the butt joint portions are disposed at the endsof the face plates 13 and 14 and projected toward the outer surface ofthe hollow shape member. The projected height of the projections 18 atjoint portion A is the same as the aforementioned example. The protrudedheight of the projections 18 at joint portion B is greater than theprotruded height at joint portion A. The size and insertion depth of therotary tools 30, 30 that are used to weld plural joint portions A and Bare all the same. Actually, if the thickness of the plate 14 where thethickness is greatest is 4 mm, the length of the small diameter portionof the rotary tool is 5 mm, so the overlap margin of the projection 18and the small diameter portion 32 is approximately 1 mm. If thethickness of the plate 13 and 14 at portion B where the thickness issmallest is 3 mm, the overlap margin of the projection 18 and the smalldiameter portion 32 is approximately 2 mm (since the length of smalldiameter portion 32 is 5 mm). Therefore, the thicknesses of the shapemembers 100, 110 and 120 including the projections 18 and the faceplates 13 and 14 are all the same.

The external shape of the large diameter portion 31 of the rotary toolis the same as that of the rotary tool 30 of joint portion A. Theexternal shape of the small diameter portion 32 is also the same as thatof the rotary tool 30 of joint portion B.

At butt joint portions A and B, one of the shape members 110 and 120 aredisposed to enter the ends of the other shape members 100 and 110. Theends of projections 18 and 18 (face plates 13 and 14) are located alongan extension of the center of plate thickness of the connecting plate16. The joint portions between the connecting plate 16 and theprojections 18 (face plates 13 and 14) are recessed. These recessedportions receive the face plates 13 and 14 of the other hollow shapemember.

The shape members 100, 110 and 120 are mounted on a jig 15, and the peaksurface of the projections 18 of the face plates 13 on the side which isnot subjected to friction stir welding at that time is in contact withthe jig 15.

According to the above-mentioned arrangement, rotary tools 30 of thesame above-mentioned size are disposed at the joint portions, andfriction stir welding operations are performed simultaneously. At jointportion A where the plate thickness is large, the insertion depth of thesmall-diameter portion of the rotary tool to the joint is the same asaccording to the prior art, and portion A is friction stir welded in amanner similar to the prior art example.

At joint portion B where the plate thickness is small, friction stirwelding is performed with the boundary between the small diameterportion 32 and the large diameter portion 31 placed 2 mm above the uppersurface of the face plate. The force of insertion of the rotary tool 30is transmitted through projections 18, 18, the connecting plate 16 andthe projections 18, 18 to the jig 15.

Thus, there is no need to vary the size of the rotary tool 30 forwelding joint portions A and B, and the insertion depth of the rotarytool 30 can be the same.

After completing the friction stir welding operation of the side of faceplate 14, the shape members 100, 110 and 120 are turned up-side down soas to have the projections on the face plate 13 protrude upward, andfriction stir welding operation is performed thereto using the samerotary tools 30 with the same insertion depth.

1. A friction stir welding method, comprising: preparing plural members,each having projections at end portions of a plate that protrude towarda direction of thickness of the plate; butting an end portion of theplate against an end portion of an adjacent plate, wherein the thicknessof the plate of at least one member is different from the thickness ofthe plate of another member, and the protruded height of the projectionson the plates at a butt joint portion where the plate thickness is largeis smaller than the protruded height of the projections on the plateswhere the plate thickness is small, and the protruded height of theprojections on the plates at a butt joint portion where the platethickness is small is larger than the protruded height of theprojections on the plates where the plate thickness is large; andinserting rotary tools of the same size with the same insertion depth tothe plates from the side having the projections, and performing frictionstir welding.
 2. The friction stir welding method according to claim 1,wherein said members are hollow shape members; and each of the hollowshape members comprises two substantially parallel face plates,connecting plates connecting the two face plates, and projections formedat width-direction-end portions of the hollow shape member.
 3. A groupof shape members for friction stir welding, comprising: plural shapemembers each having projections at end portions thereof; the pluralshape members butted against each other to form plural butt jointportions to be subjected to friction stir welding; wherein the protrudedheight of the projections at the butt joint portion where the platethickness is large is smaller than the protruded height of theprojections where the plate thickness is small, and the protruded heightof the projections at a butt joint portion where the plate thickness issmall is larger than the protruded height of the projections where theplate thickness is large.
 4. The group of shape members for frictionstir welding according to claim 3, wherein the thickness of the shapemembers including the projections and the plate are the same for all theshape members in the group.